Solar power is a clean renewable energy resource, and is becoming increasingly important for the future of this planet. Energy from the Sun is converted to electrical energy via the photoelectric effect using many photovoltaic cells in a photovoltaic (PV) panel. Power from a PV panel is direct current (DC), while modern utility grids require alternating current (AC) power. The DC power from the PV panel must be converted to AC power, of a suitable quality, and injected into the grid. A solar inverter accomplishes this task.
It would be advantageous to provide a structure, system and process to improve the efficiency of power inverters, such as for a solar panel system. Such a development would provide a significant technical advance.
To maximize the amount of power harvested, most solar inverters perform a maximum power point tracking (MPPT) algorithm. These algorithms treat an entire array of PV panels as a single entity, averaging all of the PV panels together, with a preference towards the weakest link.
It would therefore also be advantageous to provide a structure, system and process, to maximize efficiency and harvest capabilities of any solar PV system, to capitalize on profit and maximum return for the owner of the system.
Three specific examples of DC energy sources that currently have a role in distributed generation and sustainable energy systems are photovoltaic (PV) panels, fuel cell stacks, and batteries of various chemistries. These DC energy sources are all series and parallel connections of basic “cells”. These cells all operate at a low DC voltage, ranging from less than a volt (for a PV cell) to three or four volts (for a Li-Ion cell). These low voltages do not interface well to existing higher power systems, so the cells are series connected, to create modules with higher terminal voltages. Paralleled modules then supply increased power levels to an inverter, for conversion to AC power.
These long strings of cells bring with them many complications. While the current exemplary discussion is focused on PV Panels, other power systems and devices are often similarly implemented for other sources of DC power.
A problem occurs when even a single cell in a PV array is shaded or obscured. The photocurrent generated in a shaded cell may drop to around 23.2% of the other cells.
The shaded cell is reverse biased by the remaining cells in the string, while current continues to flow through the shaded cell, causing large localized power dissipation. This power is converted to heat, which in turn lowers the panel's output power capability. Bypass diodes, generally placed in parallel around each 24 cells (which may vary between manufacturers), limit the reverse bias voltage and hence the power dissipation in the shaded cell, to that generated by the surrounding half panel. However, all the power from that sub-string is lost, while current flows in the bypass diode. As well, the bypass diode wastes power from the entire string current, which flows through the panel. The output voltage of the entire string is also negatively affected, causing an even larger imbalance in the system.
Conventional module MPP currents may become unbalanced for other reasons. PV panels in a string are never identical. Because each PV panel in a series string is constrained to conduct the same current as the other PV panels in the string, the least efficient module sets the maximum string current, thereby reducing the overall efficiency of the array to the efficiency of this PV panel. For similar reasons, PV panels in a string are conventionally required to be mounted in the same orientation, and to be of identical size. This is not always possible or desirable, such as for aesthetic or other architectural reasons.
In standard solar array wiring, several series strings of solar panels are wired in parallel to each other to increase power. If there is an imbalance between these paralleled strings, current flows from the higher potential strings to the lower potential strings, instead of flowing to the inverter. Just as it is important to match the cells within a panel, it is also necessary to match the panels in a string, and then to match the strings, for maximum harvest from the solar array. If small fluctuations in environmental conditions occur, it can have a large impact on the system as a whole.
Solar inverters also “average” the entire array when they perform a conventional MPPT function. However, it is not a true average, since there is a preference that leans towards the weakest link in the system. This means that, even though some panels may be capable of supplying 100 percent of their rated power, the system will only harvest a fraction of that power, due to the averaging effect of the algorithm, and the current following through the weaker string, panel, and/or cells.
It would therefore be advantageous to provide a means for applying an algorithm that maximizes the harvest of power from a string, panel, and/or cells. Such an improvement would provide a significant advance to the efficiency and cost effectiveness of power cells structures, processes, and systems.
All public utilities in the United States have been tasked by the Federal Government to generate 25 percent of their electricity from renewable sources by 2020. Some states have mandated even higher percentages of renewable energy. For example, in 2011, California passed a law to raise the amount of renewable energy that all California utilities must use to 33 percent by 2020. While some states, such as California, already produce renewable energy through large hydropower installations, the need to increase electricity production through solar power is increasing rapidly.
Some current distributed solar panel installations, such as currently offered through Petra Solar, Inc., of South Plainfield N.J., comprise stationary brackets that are mountable to utility distribution poles, which support traditional, silicon-based, non-flexible solar panels that are locally connected to the power grid. In a typical installation, a 32 inch wide by 62 inch long silicon-based rigid solar panel is fixedly mounted at a +/−30 degree angle onto the a utility distribution pole.
Silicon panels are typically expensive, require direct light, and tolerate only a slight offset to the sun to provide power. As well, such silicon panels don't react to reflected light sources well. Furthermore, rigid silicon-based panels are fragile, and are susceptible to damage, such as by but not limited to rocks, bullets, or birds. As well, particularly when fixedly mounted at an inclined angle to a utility distribution pole, silicon-based panels are not self-cleaning, and are difficult to manually clean by hand.
It would be advantageous to provide a pole mounted solar power structure, process and system that provides enhanced power harvest, monitoring, and control for a wide variety of installations. The development of such a system would provide a significant advance to the efficiency and cost effectiveness of distributed power cells structures, processes, and systems.
One current alternative to traditional, silicon-based, non-flexible solar panels that are fixedly mounted to power distribution poles is offered through NextStep Electric, Inc., of Longmont, Colo. Flexible thin-film panels, having an adhesive backing, are wrapped directly to a power pole, and are connected to the local power grid through a micro-inverter 712. When the mounting surface of the pole surface is clean, uncluttered, and consistent, the adhesive mounting of flexible thin-film panels may provide a fast, simple, and inexpensive installation. As the flexible panels are mounted vertically to the ground, they can be considered to be at least partially self-cleaning, since less dirt accumulates on the vertical panel surfaces, and at least a portion of any accumulated dirt is cleaned through any of wind, rain, dew, or fog.
Thin-film panels are typically less fragile than silicon panels. In most cases, a thrown rock will bounce off the panel without harm. While a gunshot may penetrate the panel and cause a small loss of efficiency, it will not normally disable the panel as with silicon. Furthermore, thin-film technology is more tolerant at producing electricity from indirect and reflected light than are traditional, silicon-based solar panels.
While installations that comprise flexible thin-film panels that are attached directly to power poles may provide easier installation, improved cleaning, and tolerance to incident light direction to that of traditional, silicon-based, non-flexible solar panels, such installations are inherently limited to the available circumferential surface area of the utility pole.
It would be advantageous to provide a pole mounted solar power structure, process and system that provides a greater surface area than that of flexible thin-film panels that are attached directly to power poles, which also provides any of enhanced cleaning, robustness, monitoring, and control for a wide variety of installations. The development of such a system would provide a further significant advance.